Pre-formed curved ablation catheter

ABSTRACT

A medical device includes an insertion tube, having a longitudinal axis and having a distal end adapted for insertion through a body passage into a cavity within a body of a patient. An electrode is located on the distal end of the insertion tube and is configured to contact tissue in the cavity. A resilient member is contained within the distal end of the insertion tube and is configured, when unconstrained, to cause the distal end to bend away from the longitudinal axis in a curved shape and to straighten toward the longitudinal axis when subjected to a force.

This application is a divisional of U.S. application Ser. No. 12/636,064filed Dec. 11, 2009, the complete disclosure of which is herebyincorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to methods and devices forinvasive medical treatment, and specifically to catheters.

BACKGROUND OF THE INVENTION

Ablation of myocardial tissue is well known as a treatment for cardiacarrhythmias. In radio-frequency (RF) ablation, for example, a catheteris inserted into the heart and brought into contact with tissue at atarget location. RF energy is then applied through an electrode on thecatheter in order to create a lesion for the purpose of breakingarrhythmogenic current paths in the tissue.

Recently, circumferential ablation of the ostia of the pulmonary veinshas gained acceptance as a treatment for atrial arrhythmias, andparticularly for atrial fibrillation. For example, U.S. Pat. No.6,064,902, whose disclosure is incorporated herein by reference,describes a catheter for ablating tissue on the inner wall of a bloodvessel, such as a pulmonary vein. The tip portion of the catheter isdeflectable from a first, generally straight, configuration, in whichthe proximal and distal sections are substantially co-linear, to asecond, J-shaped, configuration in which the proximal and distalsections are generally parallel with a separation therebetweensubstantially corresponding to the inside diameter of the blood vessel.The distal end portion of the catheter is rotated about the longitudinalaxis of the catheter to cause a circumferential displacement of proximaland distal ablation electrodes on the catheter along the inner wall ofthe pulmonary vein. In this way, the electrode catheter may be used toablate a number of circumferentially-spaced sites on the inner wall ofthe pulmonary vein by ablating one or two sites at each circumferentialposition.

SUMMARY OF THE INVENTION

Embodiments of the present invention that are described hereinbelowprovide invasive devices and methods for contacting tissue within thebody with enhanced safety and efficacy.

There is therefore provided, in accordance with an embodiment of thepresent invention, a medical device, including an insertion tube, havinga longitudinal axis and having a distal end adapted for insertionthrough a body passage into a cavity within a body of a patient. Anelectrode is located on the distal end of the insertion tube and isconfigured to contact tissue in the cavity. A resilient member, whichmay include a shape memory material, is contained within the distal endof the insertion tube and is configured, when unconstrained, to causethe distal end to bend away from the longitudinal axis in a curved shapeand to straighten toward the longitudinal axis when subjected to aforce.

In a disclosed embodiment, the device includes at least one positiontransducer in the distal end of the insertion tube. The at least oneposition transducer may be configured to measure a bend angle of thedistal end of the insertion tube. In this case, the at least oneposition transducer typically includes two position transducers atdifferent longitudinal locations within the distal end of the insertiontube.

Typically, the resilient member is configured to straighten toward thelongitudinal axis when the force is applied in an inward radial force.The resilient member may be configured to buckle when the radial forceexceeds a predetermined threshold.

There is also provided, in accordance with an embodiment of the presentinvention, medical apparatus, including a sheath, which has alongitudinal axis and a distal opening and is adapted for insertionthrough a body passage into a cavity within a body of a patient. Acatheter is configured for insertion through the sheath into the cavityand has a resilient distal end that is formed so that, whenunconstrained, the distal end bends away from the longitudinal axis in acurved shape, and when subjected to a force, the distal end straightenstoward the longitudinal axis.

In a disclosed embodiment, the sheath exerts the force in an inwardradial direction so as to straighten the distal end of the catheterduring passage of the distal end through the sheath, and the distal endof the catheter assumes the curved shape after passing through thedistal opening of the sheath into the cavity. Typically, the catheter isconfigured to rotate about the axis within the sheath.

In some embodiments, the catheter includes an electrode at the distalend, which is configured to contact tissue in the cavity. The apparatusmay include a radio frequency (RF) generator, which is coupled to supplyRF energy through the catheter to the electrode so as to ablate thetissue.

In a disclosed embodiment, the catheter includes a position transducerin the distal end, and the apparatus includes a position sensing system,which is configured to communicate with the position transducer so as todetermine a location of the distal end within the body. The positionsensing system may be configured to provide an indication of a bendangle of the distal end of the catheter.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for medical treatment, including inserting asheath, having a longitudinal axis and a distal opening, through a bodypassage into a cavity within a body of a patient. A catheter is insertedinto the sheath, wherein the catheter has a resilient distal end that isformed so that, when unconstrained, the distal end bends away from thelongitudinal axis in a curved shape, and when subjected to a force, thedistal end straightens toward the longitudinal axis. The catheter isadvanced through the sheath so that the distal end of the catheterpasses through the distal opening of the sheath into the cavity andassumes the curved shape. The catheter is manipulated within the cavityso that the distal end contacts tissue in the cavity, and the catheteris moved within the sheath while the distal end contacts the tissue soas to cause the distal end to trace a desired path along the tissue.

In some embodiments, moving the catheter includes rotating the catheterabout the axis. In one embodiment, the cavity includes a blood vessel,and rotating the catheter causes the distal end to trace a circular patharound an internal circumference of the blood vessel. For example,inserting the sheath may include passing the sheath percutaneouslythrough a vascular system of the patient into a left atrium of a heartof the patient, and advancing the catheter may include positioning thedistal end of the catheter in a pulmonary vein so as to trace thecircular path within an ostium of the pulmonary vein.

In a disclosed embodiment, the method includes providing an indicationof a bending angle of the distal end of the catheter, and controlling apressure of the distal end against the tissue responsively to theindication.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic pictorial illustration of a system for ablation oftissue in the heart, in accordance with an embodiment of the presentinvention;

FIG. 2 is a schematic sectional view of a heart showing insertion of acatheter into the left atrium, in accordance with an embodiment of thepresent invention; and

FIG. 3 is a schematic side view of a catheter within the ostium of apulmonary vein, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention that are described hereinbelowprovide simple, safe, and reliable devices and methods for ablatingtissue along a selected path inside a body cavity. Some of theseembodiments are particularly suitable for ablating circumferential pathsinside a tubular structure, such as a blood vessel. The principles ofthe present invention may also be applied, however, on linear paths andin applications other than ablation.

In a disclosed embodiment, a medical device, such as a catheter,comprises an insertion tube, which is inserted through a body passageinto a body cavity, such as a chamber of the heart. The insertion tubehas an electrode at its distal tip, which makes contact with tissue inthe cavity. The distal end of the insertion tube contains a resilientmember, such as a shape memory strut, which is pre-formed so as to causethe distal end to bend away from the longitudinal axis of the insertiontube in a curved shape as long as the catheter is not constrained by aradial force. In other words, the unconstrained shape of the distal endof the catheter is bent, and the catheter assumes this shape without theuse of any sort of active steering mechanism.

When a force is applied against the distal tip of the catheter in theappropriate direction, such as an inward radial force, it causes thedistal end to straighten toward the longitudinal axis. The bend anglethus gives an indication of the force with which the catheter tip ispressing against the tissue. The distal tip of the catheter may be madestructurally weak enough to buckle if the pressure against the tissue isgreater than a certain threshold, thus giving an extra measure of safetyagainst excessive pressure that might otherwise puncture the tissue

This pre-formed curved catheter may be used to ablate tissue alongcircumferential paths inside the pulmonary veins. For this purpose, asheath is inserted into the left atrium, typically via the fossa ovalis,and is positioned coaxially with the pulmonary vein in which theablation is to be performed. The catheter is passed through the sheath(which radially constrains the catheter to remain straight while passingthrough the sheath) until the distal end of the catheter projects out ofthe sheath and into the vein. The curved shape of the distal endprojecting out of the sheath causes the electrode at the distal tip ofthe catheter to contact the inner wall of the vein. The angle and lengthof the curved end of the catheter are chosen so that the distal tippresses against the inner wall of the vein when the longitudinal axis ofthe sheath and the catheter insertion tube is aligned with the axis ofthe vein.

To carry out the ablation, an operator manipulates the catheter so thatthe electrode contacts the tissue in the ostium of the vein, and thenrotates the shaft of the catheter in the sheath while applying RF energyto the electrode. This rotation causes the electrode to move around theinner circumference of the vein in a circular path and to ablate thetissue along the path as it goes. Alternatively, the RF energy may beactuated intermittently to ablate selected points along the path.Further alternatively or in addition to this rotational movement, thephysician may apply other movements in order to trace different sorts ofpaths with the catheter.

FIG. 1 is a schematic pictorial illustration of a system 20 for ablationof tissue in a heart 26 of a patient 28, in accordance with anembodiment of the present invention. An operator 22, such as acardiologist, inserts a catheter 24 through the vascular system ofpatient 28 so that the distal end of the catheter enters a chamber ofthe patient's heart. Operator 22 advances the catheter so that itsdistal tip engages endocardial tissue at a desired location orlocations, as shown in the figures that follow. Catheter 24 is connectedby a suitable connector at its proximal end to a console 30. The consolecomprises a RF generator 36 for applying RF energy through an electrodeat the distal tip of the catheter in order to ablate the tissuecontacted by the distal tip. Alternatively or additionally, catheter 24may be used for other diagnostic and/or therapeutic functions, such asintracardiac electrical mapping or other types of ablation therapy.

In the pictured embodiment, system 20 uses magnetic position sensing todetermine position coordinates of the distal end of the catheter insideheart 26. To determine the position coordinates, a driver circuit 34 inconsole 30 drives field generators 32 to generate magnetic fields withinthe body of patient 28. Typically, field generators 32 comprise coils,which are placed below the patient's torso at known positions externalto the body. These coils generate magnetic fields in a predefinedworking volume that contains heart 26. One or more magnetic fieldsensors within the distal end of catheter 24 (as shown in FIG. 3)generate electrical signals in response to these magnetic fields. Theconsole processes these signals in order to determine the position(location and/or orientation) coordinates of the distal end of catheter24, and possibly also the bend angle, as explained below. Console 30 mayuse the coordinates in driving a display 38 to show the location andstatus of the catheter. This method of position sensing and processingis implemented, for example, in the CARTO™ system produced by BiosenseWebster Inc. (Diamond Bar, Calif.).

Alternatively or additionally, system 20 may comprise an automatedmechanism (not shown) for maneuvering and operating catheter 24 withinthe body of patient 28. Such mechanisms are typically capable ofcontrolling both the longitudinal motion (advance/retract) and therotation of catheter 24. In such embodiments, console 30 generates acontrol input for controlling the motion of the catheter based on thesignals provided by the position sensing system.

Although FIG. 1 shows a particular system configuration, other systemconfigurations may be used in alternative embodiments of the presentinvention. For example, the methods described hereinbelow may be appliedusing position transducers of other types, such as impedance-based orultrasonic position sensors. The term “position transducer” as usedherein refers to an element mounted on or in catheter 24 that causesconsole 30 to receive signals indicative of the coordinates of theelement. The position transducer may thus comprise a receiver in thecatheter, which generates a position signal to the control unit based onenergy received by the transducer; or it may comprise a transmitter,emitting energy that is sensed by a receiver external to the probe.Furthermore, the methods described hereinbelow may similarly be appliedin mapping and measurement applications using not only catheters, butalso probes of other types, both in the heart and in other body organsand regions.

FIG. 2 is a schematic sectional view of heart 26 showing insertion ofcatheter 24 into the heart, in accordance with an embodiment of thepresent invention. To insert the catheter in the pictured embodiment,the operator first passes a sheath 40 percutaneously through thevascular system and into right atrium 44 of the heart through ascendingvena cava 42. The sheath penetrates through interatrial septum 48,typically via the fossa ovalis, into left atrium 46. Alternatively,other approach paths may be used. Catheter 24 is then inserted throughthe sheath until the distal end of the catheter passes out of the distalopening at the end of the sheath into the left atrium, as shown in thefigure.

Operator 22 aligns the longitudinal axis of sheath 40 and catheter 24inside left atrium 46 with the axis of one of pulmonary veins 50. Theoperator may carry out this alignment using the position sensing methodsdescribed above, along with a pre-acquired map or image of heart 26.Alternatively or additionally, the alignment may be performed underfluoroscopic or other means of visualization. The operator inserts thedistal tip of the catheter into the target pulmonary vein and brings thecatheter tip into contact with the ostium. The operator then rotates thecatheter about its axis within the sheath in order to trace a circularpath around the internal circumference of the vein. Meanwhile, theoperator actuates RF generator 36 to ablate the tissue along the path.After completing this procedure in one pulmonary vein, the operator mayshift the sheath and catheter and repeat the procedure in one or more ofthe other pulmonary veins.

Alternatively or additionally, operator 22 may advance and/or retractcatheter 24 through sheath 40 in order to trace (and possibly ablate)linear paths along the heart wall, either in left atrium 46 orelsewhere.

The above procedures may be carried out without the use of any steeringmechanism in catheter 24: Due to the curved shape of the catheter, onlyadvancement/retraction and rotation of the catheter are required. Theabsence of an internal steering mechanism reduces the size and cost ofthe catheter relative to devices that are known in the art. As notedearlier, the above procedures may be carried out by an automatedmechanism, rather than manually by the operator as illustrated in FIG.1.

FIG. 3 is a schematic side view showing details of the distal end ofcatheter 24 within the ostium of pulmonary vein 50, in accordance withan embodiment of the present invention. Catheter 24 comprises aninsertion tube 62, which is typically made from a biocompatible plastic,such as polyurethane, and contains the functional elements of thecatheter. The longitudinal axis of the insertion tube (except for thebent distal end) is aligned with the longitudinal axis of sheath 40.

A resilient member 60 inside the distal end of insertion tube 62 ispre-formed in a bent shape. Member 60 may comprise, for example, astrut, rod or tube made from a shape memory material, such as Nitinol,which is produced so as to have this bent shape when unconstrained inits austenitic state. When an inward radial force is exerted against thebent distal end, it straightens toward the longitudinal axis. Thus,within sheath 40 catheter 24 is held straight by the sheath itself.Pressure of the catheter tip against the ostium of vein 50 (or againstother tissue) will also tend to straighten the distal end of thecatheter. Resilient member 60 may be made structurally weak enough tobuckle if the pressure against the catheter tip is greater than acertain predetermined threshold, thus giving an extra measure of safetyagainst excessive pressure that could otherwise puncture the vein orheart wall.

Catheter 24 comprises an electrode 64 at the distal tip of insertiontube 62. This electrode is connected by a conductor (not shown) runningthrough the catheter to RF generator 36, which thus provides RF energyto ablate the tissue with which the electrode is in contact. Rotatingcatheter 24 about its axis, as illustrated by the circular arrow in FIG.3, causes electrode 64 to trace a circular path around the innercircumference of the ostium of vein 50. Operator 22 is thus able tocreate a circular ablation lesion easily and reliably.

Catheter 24 comprises position sensors 66 and 68 at differentlongitudinal locations within the distal end of insertion tube 62. Inthe embodiment shown in FIG. 1 and described above, sensors 66 and 68comprise coils, which sense the magnetic fields produced by fieldgenerators 32 and output signals to console 30. The console processthese signals in order to find the location and orientation coordinatesof the coils. The difference between the orientations of sensors 66 and68 indicates the bend angle (or equivalently, the curvature) of thedistal end of the catheter. Alternatively, the bend angle may bemeasured using position transducers or bend sensors of other types.Additionally or alternatively, operator 22 may observe the bend anglefluoroscopically.

Reduction of the bend angle (straightening of the distal end) relativeto the bend angle of the distal end when unconstrained is indicative ofthe radial force exerted on the distal tip of catheter 24 by the tissuewith which it is in contact: The harder the operator presses the tipradially against the tissue, the smaller will be the bend angle. Console30 may present an indication of the bend angle, such as a graphicalrepresentation of the distal end of the catheter, on display 38.Operator 22 can then control the radial pressure exerted by the catheteragainst the tissue in heart 26 so that the bend angle remains within asuitable range. Typically, a small degree of unbending of the distal endof the catheter is desirable to ensure that electrode 64 contacts thetissue firmly; but too much unbending is to be avoided in order toprevent puncturing of the tissue due to excessive pressure.Alternatively or additionally, the bend angle of the catheter may bemonitored and controlled automatically.

Although the above embodiments relate specifically to treatment in andaround the pulmonary veins, the design features of catheter 24 and ofsystem 20 generally may also be used for treatment inside other veinsand arteries, as well as in other sorts of body cavities, both tubularand of other shapes. It will thus be appreciated that the embodimentsdescribed above are cited by way of example, and that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofwhich would occur to persons skilled in the art upon reading theforegoing description and which are not disclosed in the prior art.

What is claimed is:
 1. Medical apparatus, comprising: a sheath, whichhas a longitudinal axis and a distal opening and is adapted forinsertion through a body passage into a cavity within a body of apatient; and a catheter, which is configured for insertion through thesheath into the cavity and which has a resilient distal end that isformed so that, when unconstrained, the distal end bends away from thelongitudinal axis in a curved shape, and when subjected to a force, thedistal end straightens toward the longitudinal axis.
 2. The apparatusaccording to claim 1, wherein the sheath exerts the force in an inwardradial direction so as to straighten the distal end of the catheterduring passage of the distal end through the sheath, and wherein thedistal end of the catheter assumes the curved shape after passingthrough the distal opening of the sheath into the cavity.
 3. Theapparatus according to claim 2, wherein the catheter is configured torotate about the axis within the sheath.
 4. The apparatus according toclaim 1, wherein the catheter comprises an electrode at the distal end,which is configured to contact tissue in the cavity.
 5. The apparatusaccording to claim 4, and comprising a radio frequency (RF) generator,which is coupled to supply RF energy through the catheter to theelectrode so as to ablate the tissue.
 6. The apparatus according toclaim 1, wherein the catheter comprises a position transducer in thedistal end, and wherein the apparatus comprises a position sensingsystem, which is configured to communicate with the position transducerso as to determine a location of the distal end within the body.
 7. Theapparatus according to claim 6, wherein the position sensing system isconfigured to provide an indication of a bend angle of the distal end ofthe catheter.